The present invention relates to a seal for rotating shafts, which includes a preformed ring made of rubber or similar plastomers, and is inserted in ring slots in order to seal shafts or similar machine parts. The oil present in the machine is held back, and no dirt or dust from outside enters into the machine. Such seals are especially used in motor vehicles.
Such a seal is described in German Published Patent Application No. 2 333 208. The working planes of the lip-seal sealing edge and the working plane of the annular helical spring are staggered and so that the working plane of the annular helical spring is shifted toward the atmospheric side of the seal. The result is a value X, which is also referred to as value R, and is positive. This is regarded as being necessary for achieving a good seal and preventing losses of operating oil. To improve the effectiveness of the seal, the air side of the lip seal is provided with a concave, preformed surface. This forms a sharply delimited angle between the sealing edge and the shaft surface. This angle is relatively large, and is between 50 and 80 degrees. The opposite angle directed towards the hydraulics is selected to be considerably smaller, such as less than 10 degrees, or even 5 degrees, but not greater than 20 degrees. However, such a seal does not fulfill the set requirements in many cases. At higher hydraulic pressures, and also at higher shaft speeds, there is a danger of these seals running dry and being subject to a high degree of wear.
German Published Patent Application No. 37 42 080 describes another type of seal, in which the object is to sufficiently lubricate the sealing strip, and therefore, to increase the service life. The seal is used for low-viscosity media, e.g., water, the pressure of the water being higher than the pressure of the gaseous medium on the other side of the seal. In order to direct the water under and through the sealing lip, the angles between the sealing-lip surfaces and the shaft are selected to be very small. The lower the viscosity of the liquid, the smaller the angle selected. In this case, the angle should be at most 12 degrees. In addition, hydrodynamic conveying grooves are disposed on the lip, which are designed to convey the liquid medium from the higher-pressure to the lower-pressure medium. The working plane of the annular helical spring has a negative value with respect to the working plane of the sealing edge. This is necessary for the pumping action of the seal. However, it leads to considerable amounts of water being directed through the seal. Such a measure is acceptable as long as the liquid medium is water, e.g., as in drive shafts of ships. However, this is not acceptable for drive motors.
Therefore, it is an object of the present invention to provide a radial shaft seal, in which the sealing lip does not experience wear, leakage is prevented to a great extent, and the sealing lip is effectively lubricated.
The seal may be used in areas where the hydraulic pressure is considerably higher than atmospheric pressure. The seal may be able to withstand hydraulic pressures of over 5 bar and up to 10 bar, depending on the rotational speed. The seal may also be usable at all viscosities.
In the case of a radial shaft seal, which is made of a ring-shaped, metal supporting body and a sealing lip disposed on it, to separate a hydraulic side that is particularly under high pressure, from an atmospheric side, in which case the sealing lip is pressed onto the shaft by an annular helical spring, the object of the present invention is achieved in that, in an uninstalled sealing ring, the working plane of the annular helical. spring has a value X that is less than zero with respect to the working plane of the sealing edge, and in the case of an installed sealing ring, the two working planes are approximately coplanar.
During the manufacture of the sealing ring, care should be taken that the value X is between 0 and 2 mm, preferably between 0 and 0.8 mm, so that it always has a negative value. This value X may be approximately 1% of the sealing-ring inner diameter. By installing the sealing ring, i.e., fitting it onto the shaft, the two mentioned planes are moved toward one another, and come to rest approximately one over another. It has been shown that this manner of installing the sealing ring minimizes leakage. Thus, the lubrication is effective, and wear is prevented at the sealing lip.
The angles between the sealing-lip surfaces and the shaft are formed so that angle alpha between the sealing-lip surface facing the atmospheric side and the longitudinal section of the shaft is greater than angle beta between the sealing-lip surface facing the hydraulic side and the longitudinal section of the shaft. It was determined that this angle configuration minimizes the effective sealing area between the lip and the shaft. Angle beta is selected to be 15 to 30 degrees, preferably 17 to 22 degrees, and angle alpha is selected to be 35 to 65 degrees, preferably 45 to 60 degrees.
Starting from the sealing lip, a grease chamber may be positioned in the direction of the atmospheric side. This grease chamber may be terminated by an additional sealing lip, which is integrally connected to the sealing lip. The sealing-lip surface directed toward the atmospheric side may be subdivided into two sections, the first section forming angle alpha with the shaft, and the second section having angle (gamma), which is approximately half as large as angle beta.
Angles alpha and beta are approximately equal in an installed sealing ring. They then assume values between 20 and 50 degrees, and are preferably 30 degrees.
The sealing function of a sealing ring designed in this manner may be further improved by so-called dynamic sealing aids (swirl or helical patterns) which, for example, may be arranged as raised patterns or structures on the sealing-lip surface, in the direction of the atmospheric side.